The present invention relates to an electron gun assembly for a cathode ray tube (CRT), and is particularly concerned with shapes of an electron-stream extractor electrode (namely, accelerating electrode) and a focusing electrode.
In general, an electron gun assembly for a CRT is assembled in the following procedures. First, cathode electrodes each formed into a plate-like shape, tube-like shape, cap-like shape, or the like, a control electrode, an electron-stream extractor electrode, a focusing electrode, and an anode electrode are laid on one another with spacers placed in between. Next, a surface with holes of the focusing electrode (Each of the holes allows a stream of the electrons to pass through.) is placed on a reference position. This is because a position of the surface with holes of the focusing electrode would have the greatest effect on the performance of the electron gun assembly. Next, pressure is applied from the side of a three-electrode portion (the cathode electrodes, the control electrode, and the electron-stream extractor electrode) and from the side of the main lens (the focusing electrode). Then, the periphery of these electrodes is secured by heated glass material such as multiform glass of Asahi Glass Corporation.
FIG. 6 to FIG. 9 show the electron-stream extractor electrode 30 and the focusing electrode 40 described above. FIG. 6 is a horizontal sectional view showing the electron-stream extractor electrode 30 and the focusing electrode 40, and FIG. 7 is a vertical sectional view taken along a line S6xe2x80x94S6 of FIG. 6. Moreover, FIG. 8 is a front view of the electron-stream extractor electrode 30 when viewed from the focusing electrode 40, and FIG. 9 is a front view of the focusing electrode 40 when viewed from the electron-stream extractor electrode 30.
As shown in the figures, the electron-stream extractor electrode 30 has holes 31, 32, and 33, each of which allows a stream of the electrons (namely, an electron beam) to pass through, and which are arranged in an in-line direction (X direction). Further, the electron-stream extractor electrode 30 has circular depressions 34, 35, and 36 that are formed around the holes 31, 32, and 33 by the coining process. The depression 34 is formed in such a place that a center position is disposed inside a center position of the hole 31. The depression 36 is formed in such a place that a center position is disposed inside a center position of the hole 33. In addition, as shown in the figures, the focusing electrode 40 has holes 41, 42, and 43, each of which allows the stream of the electrons to pass through, and which are arranged in the in-line direction. The holes 41, 42, and 43 are formed at the bottom of the rectangular depressed portions 44, 45, and 46 made by the drawing process, each of which functions as a quadrupole lens.
The electron-stream extractor electrode 30 and the focusing electrode 40 described above form electrostatic lenses, as indicated by broken lines in FIG. 6, which adjust the traveling directions (courses) and the cross sectional shapes of the electron beams. The courses of the electron beams can be adjusted by changing the center positions of the depressions 34 and 36, and the shapes of the electron beams can be adjusted by changing the width and length (namely, aspect ratio) of the rectangular depressed portions 44, 45, and 46 respectively.
As has been described above, in the conventional electron gun assembly, the bottoms of the rectangular depressed portions 44, 45, and 46 of the focusing electrode 40 are used as the reference positions when the electrodes are assembled. However, the drawing process for forming the rectangular depressed portions 44, 45, and 46 produces slight machining variations in depth, position, and size of the bottoms of the rectangular depressed portions 44, 45, and 46, depending on the product. Accordingly, it has been difficult to reduce variations in performance depending on the product, resulting from machining errors of the conventional electron gun assembly.
It is an object of the present invention to provide an electron gun assembly for a CRT that can reduce variations in performance depending on the product, resulting from machining variations.
According to the present invention, an electron gun assembly for a CRT includes: at least one cathode electrode which emits electrons; a control electrode which controls traveling directions of the electrons emitted from the cathode electrode, thereby producing three streams of the electrons; an electron-stream extractor electrode which accelerates the three streams of the electrons; a focusing electrode which focuses the three streams of the electrons accelerated by the electron-stream extractor electrode; and an anode electrode which accelerates the three streams of the electrons focused by the focusing electrode. The electron-stream extractor electrode includes first, second, and third holes, each of which allows one of the three streams of the electrons produced by the control electrode to pass through. The focusing electrode includes a surface which faces the electron-stream extractor electrode, the surface including fourth, fifth, and sixth holes, each of which allows one of the three streams of the electrons accelerated by the electron-stream extractor electrode to pass through, the fourth, fifth, and sixth holes facing the first, second, and third holes, respectively. At least one of the fourth, fifth, and sixth holes of the focusing electrode includes a substantially rectangular opening and a substantially semicircular opening, one side of the substantially rectangular opening being connected to a straight line segment of the substantially semicircular opening.